1. Field of the Invention
This invention relates to working vehicles such as tractors. More particularly, the invention relates to a steering apparatus mounted on such a working vehicle to steer the vehicle by changing directions relative to a vehicle body of right and left wheels.
2. Description of the Related Art
With an agricultural tractor as an example of working vehicles, a turn may be made with a small turning radius on a headland to provide advantages of making the headland small and moving quickly along the headland. For this purpose, a steering technique has been proposed as disclosed in Japanese Laying-open Utility Model Publication S56-36574 and U.S. Pat. No. 5,046,577. In this steering technique, wheels are supported at opposite ends of an axle member to be pivotable about vertical axes, and the axle member in turn is supported at a midpoint transversely of a vehicle body to be pivotable about a vertical axis. The vehicle is steered by changing directions relative to the vehicle body of the axle member and directions relative to the axle member of the right and left wheels. Thus, directions relative to the vehicle body of the wheels are changed by the combination of directional changes relative to the axle member of the wheels and directional changes relative to the vehicle body of the axle member. Compared with a case of employing only the directional changes relative to the axle member of the wheels, this steering mode provides a small turning radius even with an increased maximum steering angle of the wheels.
With the conventional steering technique noted above, when the vehicle is steered, the right and left wheels change directions relative to the vehicle body while sliding to large extents sideways on the ground. To enable the right and left wheels to roll relative to the vehicle body, the axle member has to be supported by the vehicle body to be pivotable also about an axis extending longitudinally of the vehicle body. This requires a complicated construction for attaching the axle member to the vehicle body, and this attaching construction requires a high degree of supporting strength, resulting in disadvantages in terms of cost and weight.
The object of this invention is to provide a steering apparatus for a working vehicle, which not only can steer wheels by increased steering angles but can reduce sideways sliding of the wheels and enable rolling of the wheels with a relatively inexpensive and lightweight construction.
The above object is fulfilled, according to this invention by a working vehicle comprising:
a vehicle body;
a pair of right and left dirigible wheels each having an axle;
a steering wheel for steering the pair of right and left dirigible wheels;
a pair of wheel supports arranged in right and left positions of the vehicle body;
intermediate cases each supported by one of the wheel supports to be pivotable relative to the one of the wheel supports about a first steering axis extending substantially vertically;
axle cases each attached to a side of one of the intermediate cases opposed to one of the dirigible wheels for supporting the one of the dirigible wheels on one of the axles, each of the axle cases being pivotable relative to one of the intermediate cases about a second steering axis extending substantially vertically; and
a steering control mechanism operable in response to turning of the steering wheel for swinging each of the intermediate cases about the first steering axis and swinging each of the axle cases about the second steering axis, thereby steering the pair of dirigible wheels relative to the vehicle body.
The above construction provides the following advantages. When the steering wheel is turned, the steering control mechanism swings each of the right and left intermediate cases the first steering axis relative to the wheel support, and swings each of the right and left axle cases about the second steering axis relative to one of the intermediate cases. The direction relative to the vehicle body of the right and left wheels changes by both changes in the direction relative to the vehicle body of the intermediate cases and in the direction relative to the intermediate cases of the wheels. This results in a larger maximum steering angle for steering the right and left wheels than where the wheels are steered only about the second steering axes.
Further, each intermediate case is pivotably supported by a wheel support disposed at the left or right side of the vehicle body. The second steering axis serves as a pivotal axis of each dirigible wheel. The first steering axis provides a fulcrum about which the pivotal axis of this wheel is movable longitudinally of the vehicle body. That is, the distance from the fulcrum of movement to the wheel pivotal axis is shorter than the distance from the pivotal axis of an axle member which is a conventional fulcrum of movement to the wheel pivotal axis. Thus, the right and left wheels, when steered, slide sideways over reduced distances over the ground than in the prior art.
An axle member is supported by the vehicle body to be pivotable about a longitudinal axis of the vehicle body, and left wheel support is formed at one end of the axle member and a right wheel support formed at the other end of the axle member. Then, while the axle member is connected in an intermediate position thereof to the vehicle body only to be pivotable about the longitudinal axis of the vehicle body, the right and left wheels change directions by swinging about the second steering axes of the axle cases and swinging about the first steering axis of the intermediate cases, and roll (i.e. swing from side to side) relative to the vehicle body through the axle cases, intermediate cases and axle member.
Thus, with the steering apparatus for a working vehicle according to this invention, changes in the direction relative to the vehicle body of the right and left wheels are effected with larger steering angles than where the right and left wheels are swung only about the second steering axes. The vehicle may be turned with a small turning radius on a headland to diminish the headland. The vehicle may engage in an agricultural operation while running with advantage, such as moving quickly from a finishing point of a preceding patch to a starting point of a next patch.
Moreover, the vehicle may be steered while suppressing side slipping of the wheels on the ground to be less than in the prior art where the axle member swings in the middle position transversely of the vehicle body. Thus the vehicle may run steadily with a reduced chance of sideslipping and other defective running.
Further, the right and left wheels may roll from side to side to maintain the running vehicle body substantially horizontal regardless of irregularities or slopes of the ground. This is achieved by attaching the axle member forming the right and left wheel supports to the vehicle body through the simple mounting structure that only enables the axle member to swing up and down relative to the vehicle body. Thus, the apparatus according to this invention is inexpensive and lightweight.
In the above construction, when the right and left dirigible wheels are in a straight moving state, the second steering axis, preferably, is displaced from the first steering axis longitudinally of the vehicle body.
When changing the direction of a dirigible wheel relative to the vehicle body, the front or rear end of the wheel pivoting about the second steering axis would approach an inward member such as the vehicle body and eventually contact the inward member. Assume that the dirigible wheel is a front wheel and the second steering axis is displaced forwardly from the first steering axis when the wheel is in a straight moving state. When the wheel is turned outward from the straight moving state, the ground-engaging point of the wheel initially moves about the second steering axis and outwardly of the vehicle body. On the other hand, where the second steering axis is aligned with the first steering axis transversely of the vehicle body, the ground-engaging point of the wheel constantly moves about the second steering axis and inwardly of the vehicle body when the wheel is turned outward from the straight moving state. It follows that the former provides a larger angle for swinging the intermediate case about the first steering axis while the wheel moves from the straight running position to a position contacting the inward member.
Assume that the dirigible wheel is a rear wheel and the second steering axis is displaced rearwardly from the first steering axis when the wheel is in a straight moving state. When the wheel is turned outward from the straight moving state, the ground-engaging point of the wheel initially moves about the second steering axis and outwardly of the vehicle body. On the other hand, where the second steering axis is aligned with the first steering axis transversely of the vehicle body, the ground-engaging point of the wheel constantly moves about the second steering axis and inwardly of the vehicle body when the wheel is turned outward from the straight moving state. It follows that the former provides a larger angle for swinging the intermediate case about the first steering axis while the wheel moves from the straight running position to a position contacting the inward member. Thus, the right and left wheels may be steered by a larger maximum steering angle where the second steering axis is displaced from the first steering axis longitudinally of the vehicle body than where the second steering axis is aligned with the first steering axis transversely of the vehicle body when the wheels are in a straight running state.
With the construction according to this invention, the vehicle may be turned with a small turning radius also by the arrangement of the first steering axis and the second steering axis to increase the steering angle of the right and left wheels. This provides an advantage of further diminishing a headland.
Preferably, the steering control mechanism includes a control mechanism for linking one of the axle case and the intermediate case to the steering wheel, and an interlock mechanism for interlocking the other of the axle case and the intermediate case to the control mechanism.
When the steering wheel is turned, the right and left wheels are steered by the control mechanism swinging one of the axle case and the intermediate case and the interlock mechanism swinging the other in response to the swinging of one of the axle case and the intermediate case. That is, compared with linking the intermediate case and the axle case individually to the steering wheel, the steering control mechanism is simple in terms of both control and construction to control the axle cases and intermediate cases with turning of the steering wheel.
Thus, steering controls may be performed with the increased maximum steering angle of the right and left wheels with the steering control mechanism simple in construction and inexpensive to manufacture.
In one preferred embodiment of the invention, the interlock mechanism is the link type including a pivot link extending from the other of the axle case and the intermediate case to the wheel support.
By properly selecting a length or mounting angle of the pivot link, the intermediate case and axle case may be interlocked so that, for example, the axle case may swing in response to swinging of the intermediate case, and the axle case swings with swinging by unit angle of the intermediate case, by different angles according to positions of the intermediate case. The wheel may be steered by pivoting about the second steering axis in response to turning by unit angle of the steering wheel, to change directions relative to the vehicle body by different angles for a range of small steering angles and a range of large steering angles.
Thus, the link may determine whether a large change or a small change occurs in the direction of the wheel for an amount of turning of the steering wheel. The vehicle may make a small turn with the wheels turned by a large degree by turning the wheel steering only slightly. The vehicle may run without meandering, with little change occurring in the directions the wheels when the steering wheel is turned slightly. Such modes may be realized with a simple construction.
In a preferred embodiment of the invention, the first steering axis and the second steering axis extend parallel to each other, the dirigible wheels being drive wheels, and a transmission system for transmitting drive from the vehicle body to each of the dirigible wheels includes a gear transmission having a first spur gear rotatable about the first steering axis and a second spur gear rotatable about the second steering axis.
This construction provides the following advantages. When the steering apparatus is operated, the right and left intermediate cases swing about the first steering axes relative to the proximal drive case unit, and the right and left distal drive case units swing about the second steering axes relative to the intermediate cases, thereby placing the right and left wheels in a desired direction relative to the vehicle body to steer the vehicle. In a conventional construction, the wheels may be set to a desired direction relative to the vehicle body by turning each wheel only about one steering axis, or by swinging an axle supporting wheels at right and left ends thereof relative to the vehicle body and swinging the wheels relative to the axle. Compared with such a construction, the vehicle may be steered by turning the wheels by a desired maximum steering angle while diminishing a space required between each wheel and the vehicle body for turning the wheels by the desired maximum steering angle, and diminishing a maximum distance of movement of each wheel laterally of the vehicle body when the wheel is steered by the desired maximum steering angle.
Where drive is transmitted to the wheels by using gears rotatable on the first steering axis and the second steering axis, drive transmission is achieved with little possibility of defective transmission such as unequal speed transmission while enabling smooth swinging of the intermediate cases and distal drive case units. Where the first and second steering axes are nonparallel, bevel gear rotatable on the respective axes must be employed. Where the first and second steering axes are parallel, less expensive spur gears may be employed as gears rotatable on the respective steering axes.
The gear transmission may be mounted in the intermediate case, and may have a first transmission shaft rotatable about the first steering axis and interlocked at a lower end thereof to a second transmission shaft rotatable about the second steering axis.
With this construction, where the wheel drive case provides a lubricating oil bath therein, the gear mechanism may reliably be immersed in the oil bath for lubrication. Thus, this construction has an advantage that the transmission mechanism may be lubricated effectively.
In addition, the axle may have a large diameter spur gear mounted to be rotatable therewith, the large diameter spur gear being interlocked to an intermediate transmission shaft through a small diameter spur gear, the intermediate transmission shaft being interlocked to the second transmission shaft through a pair of bevel gears, whereby the axle is interlocked to the second transmission shaft with a decelerating effect.
Generally a pair of bevel gears are used as such a reduction device. This invention provides an intermediate transmission shaft interlocked through a small diameter spur gear to a large diameter spur gear mounted on the axle to be rotatable therewith. The intermediate transmission shaft and the second transmission shaft are interlocked through a pair of bevel gears. In this way, drive is transmitted from the second transmission shaft to the axle as decelerated by two stages.
Thus, drive may be transmitted from the small diameter spur gear to the large diameter spur gear with a small reduction ratio, and the large diameter spur gear may be reduced in size compared with the case of transmission only through a pair of bevel gears. As a result, a portion of the distal drive case unit extending into the wheel may include a circular main portion housing the large diameter spur gear, and a local projection projecting radially outwardly and housing the intermediate transmission shaft. The main portion may be reduced in size to enlarge a major portion of the space between the wheel and outer peripheries of the distal dive case unit, thereby suppressing clogging of the space with soil.